Descriptions of Crinoids from the Upper Suhcarhoniferous. 327 



tinuous between the rajs from the basal plates to the dome, and the 

 sutures between the arms continuous from the first subdivision of the 

 raj'S, or from the apex of the brachials upward. Thus the first arms, 

 or the contiguous ones over the brachials, are the longest in each v^y. 

 This is the same arrangement of the arms that we have in typical 

 Zeacrinus. 



The Azygous area. — This consists of five hexagonal plates, arranged 

 in two series as exposed, the lower plate upon the right. In section 

 these plates are seen to be the base of a dome-like support of the 

 ventral sac, which, as may be seen from figure 6, where the azygous 

 plates are represented upon the right, is continuous over the lower 

 part of the body cavit}', arching in all that part below the upper 

 surface of the radials. These plates are greatly thickened, a fact 

 which, as well as their articulation with the inner ledge of the brachi- 

 als, is not correctly represented in the figure. The lower extremit}^ 

 of the ventral sac is inclined to that part of the dome adjacent 

 to the azygous side, to such an extent, that the azygous plates 

 'are practically continuous with the walls of the lower extremitj^ of 

 that organ. The}^ are, consequently, the exposed lower part of its 

 parietes here as in other genera. 



The Ventral Sac. — This is composed of plates which are mostly 

 hexagonal, thicker above and below than in its central part, and 

 which have their sutures perforated at the angles by pores communi- 

 cating with the interior (see fig. 6a). 



This structure tapers from the lower extremity to a constriction 

 somewhat below the middle, whence it widens outward to the top, 

 wheve its diameter is three times that of the middle portion. The 

 cavit}' inside has the same form as the exterior, being very much con- 

 tracted in the center, and widened above and below. No connection 

 of this cavity with that below it has yet been discovered. The top of 

 this sac is covered with a set ot quite regularly hexagonal plates, 

 which do not, as may be seen by figure 3, exhibit an}' definite order 

 of arrangement, nor do IhQj agree in number or size in diff'erent 

 individuals that may readily be referred to this species. The outer 

 plates are terminated b}^ spines which project far beyond the peripherj'- 

 of the arms, and are somewhat bent downward, or arched toward the 

 base like the ribs of an umbrella, though in a less degree. The}'' 

 were verj'^ delicate, and are rarely preserved upon specimens not im- 

 bedded in the matrix. In specimens having the sac roofed by 24 

 plates, there are twelve of these marginal spiniferous ones. 



The Pinnulce. — These appear to be short and stout, as described by 



